The present invention is related to electrical circuits for recovering clock signals from a stream of transmitted digital signals and, more particularly, to circuits for detecting the edges of high-frequency, i.e., microwave, digital signals.
In the transmission of digital signals, the recovery at the receiver of the transmitter clock signal from a stream of incoming signals is an important function. The clock signal is required for the correct marking of each signal and permits the proper determination of the signal.
Present day “wired” communications are transmitting signals at faster and faster signal rates and optical fibers are typically used to carry such high-speed signals. An emerging standard for signal transmission over an optical fiber is OC-768 (Optical Carrier level-768) by which 40 gigabits per second are transmitted over SONET (Synchronous Optical NETwork) networks. The electrical signals resulting from these optical signals are at microwave frequencies which often induce resonances in the receiving circuit. Such resonances introduce undesired jitter and noise into electrical circuits, including circuits for recovering the clock signal from the transmitted signals.
There is, therefore, a need for clock signal recovery circuits which can operate effectively on high-frequency signals in emerging OC-768 systems.